The process of grilling or frying food produces by-products from the cooking process such as smoke and odors which are conventionally removed through an exhaust ventilation system. In a commerical cooking establishment, the exhaust ventilation system generally includes a vented hood extending over the area in which the food is grilled or fried and an exhaust fan motor for drawing the smoke and the like from the vented hood and up through the ventilation ducting to the exterior of the building.
The conventional ventilation exhaust system described above draws a considerable quantity of air from the interior of the building along with the unwanted cooking odors and smoke. As a result, the air heated or cooled by the air conditioning system of the building is also exhausted to the outside, causing the thermostat of the air conditioner to run the air conditioning system to replace the exhausted air. The resultant inefficient operation of the air conditioning system creates an added expense of operation for the owner of the building through higher utility bills, and more importantly it needlessly wastes valuable energy.
Numerous attempts have been made in the past to overcome these difficulties associated with an exhaust ventilation system. One approach has been to install a fresh air blower with an exhaust vent located near the cooking station, so that a quantity of outside air is blown into the cooking area to be exhausted along with the smoke and odors instead of the building's air conditioning. Such a system has proven unsatisfactory in periods of extreme hot or cold outside temperatures, since the introduction of such air into the interior of the building offsets the air conditioning system causing it to run more often and consume more energy.
Other systems have been heretofore developed for automatically operating a cooking area ventilation system in response to detecting smoke or particles emitted from the cooking area, such as U.S. Pat. Nos. 3,625,135 and 3,826,180. Other exhaust fan systems have been devised which are automatically operable in response to a pressure sensitive switch in the gas burner for the cooking stove, U.S. Pat. No. 2,182,106. However, such prior devices are not entirely adequate to overcome the problem, since they often involve complicated and expensive circuitry and detection devices, and these devices are normally mounted within the vent and are susceptible to damage from small grease fires which sometimes occur within the cooking area. In addition, grease accumulates on such detection devices mounted within the vent and require frequent maintenance to prevent the system from being rendered inoperative by such accumulation of grease.
A need has thus arisen for a practical exhaust ventilation control system which reduces the unnecessary running time for the exhaust fan and the associated increased energy consumption of the system air conditioning the interior of the building. In addition, there is a need for a ventilation control system which dependable to operate, relatively inexpensive, and easy to install.